1. Field
The following description relates to a bidirectional optical transceiver, and more particularly, to a technology for preventing thermal, electrical or optical crosstalk in a bidirectional optical transceiver which provides reception and transmission using one optical line.
2. Description of the Related Art
In a passive optical network, such as a Gigabit PON (GPON), an Ethernet PON (EPON), a Wavelength Division multiplexing PON (WDPON) and so on, an Optical Network Unit (ONU) and Optical Line Terminal (OLT) each includes an optical-transmitting module and an optical-receiving module. A bidirectional optical transceiver is an apparatus in which an optical-transmitting module and an optical-receiving module are packaged into one body to perform transmission and reception through one optical line.
FIG. 1 illustrates a conventional TO-can type bidirectional optical transceiver. As illustrated in FIG. 1, in a bidirectional optical transceiver, an optical-transmitting module 10, an optical-receiving module 20 and an optical line 30 are arranged in a T-shaped form, and an optical system 40 is located in the center of a housing 50 which has a O-shaped form.
The optical-transmitting module 10 includes a laser diode 11 and a monitoring diode 12, the optical-receiving module 20 includes a photodiode 21 and a pre-amplifier 22, the optical line 30 may be an optical fiber suitable for receiving/transmitting optical signals, and the optical system 40 includes an optical filter 41 inclined at 45 degrees, a first lens 42, a second lens 43 and a third lens 44.
A beam transmitted from the laser diode 11 of the optical-transmitting module 10 is converted into collimated light through the first lens 42, is input to and passes through the optical filter 41, and is directed towards the second lens 43. The second lens 43 focuses the collimated light which is penetrated by the optical filter 41 and outputs the focused beam to the optical line 30. The beam is externally transmitted through the optical line 30, so that an optical signal is transmitted.
Meanwhile, a beam received through the optical line 30 is converted into collimated light by the second lens 43 and input to the optical filter 41, and then the collimated light is reflected by the optical filter 41 towards the third lens 44. The third lens 44 focuses the collimated light reflected by the optical filter 41 and outputs the focused beam to the photodiode 21 of the optical-receiving module 20. The beam is photoelectrically transformed by the photodiode 21 and voltage-amplified and output by the pre-amplifier 22, so that an optical signal is received.
At this time, the monitoring photodiode 12 of the optical-transmitting module 10 monitors the optical output of the laser diode 11 in real time and outputs an optical monitoring signal to an external driving circuit (not shown), and the external driving circuit controls input current of the laser diode 11 according to the optical output monitoring signal from the photodiode 12, thus maintaining the optical output of the laser diode 11 at a constant level.
The TO-can type bidirectional optical transceiver receives a current signal modulated according to a direct modulation method from the external driving circuit and performs on/off operations according to the received current signal. At this time, since the driving current of the driving circuit is transmitted to the laser diode 11 through transmission lines of a Printed Circuit Board (PCB) on which electronic devices of the optical-transmitting module 10 are mounted and through lead wires of the TO-can type bidirectional optical transceiver, the current transfer path may reach 10 mm or more in consideration of areas for soldering.
Accordingly, current leakage, electrical crosstalk and so on between peripheral transmission lines and electronic circuits occur, which makes high-speed modulation exceeding 10 Gbps difficult. Therefore, in order to achieve high-speed transmission and prevent current leakage and electrical crosstalk, the driving circuit has to be placed close to the laser diode 11 of the bidirectional optical transceiver.
However, the conventional TO-can type bidirectional optical transceiver has a cylindrical structure in which a housing including a laser diode therein cannot efficiently transfer internally generated heat to an external heat sink. Accordingly, the present inventor has performed research into a bidirectional optical transceiver with a stacked structure capable of preventing thermal and electrical crosstalk by improving heat dissipation characteristics.